1. Field of the Invention
This invention relates to a method for reactivating or regenerating a noble metal catalyst by oxidation treatment.
2. Description of the Prior Art
Mono methyl hydrazine (MMH) and unsymmetrical dimethylhydrazine (UDMH), due to the ability of these compounds to provide hypergolic ignition upon contact with a strong oxidizer, represent important liquid propellant fuels, particularly for space vehicles. Although there are several routes available for the production of these compounds, all, however, involve problems of one type or another.
For example, the most expedient process for producing UDMH consists of hydrogenating nitrosodimethylamine in turn obtained by nitrosating dimethylamine. This process, however, has been banned for all practical purposes because of the extremely potent carcinogenic nature of the nitrosodimethylamine intermediate. A currently practiced process for producing MMH is in accordance with a modified Raschig synthesis involving the in situ generation of mono-chloramine and subsequent reaction with monomethyl amine. The principal disadvantage of this process is that it is very energy intensive.
The remaining process commercially applicable for producing UDMH as well as MMH, and the process to which the present invention relates, consists of the reductive alkylation of an acid hydrazide with formaldehyde in the presence of hydrogen and a suitable hydrogenation catalyst and subsequent base hydrolysis or hydrozinolysis of the resultant alkylate. In order to realize an acceptable yield of product in accordance with the foregoing process, it is necessary to use either palladium or platinum as the catalyst. Unfortunately, however, the reaction environment is such that the indicated catalysts are prone to become poisoned and lose substantially all activity after completing an initial alkylation sequence. It is therefore the object of this invention to provide a facile method for restoring the activity of said catalyst values to essentially their initial pristine level following each use thereof as aforesaid.